Mythbusters tire pressure testing: +5 psi = 6% fuel savings

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DaveEV

DaveEV

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Linking to the Ecomodder forum where I found this nugget of info:

http://ecomodder.com/forum/showthread.php/mythbusters-tests-tyre-tire-pressure-17151.html

Summary of results: 2003-2007 Ford Taurus, tested at these pressures:

Control, 35psi (manufacturer recomendation)
tyres at 10psi = 3.7% increase in consumption
tyres at 30psi = 1.2% increase in consumption
tyres at 40psi = 6.2% decrease in consumption
tyres at 60psi = 7.6% decrease in consumption
Click to expand...
Fuel consumption didn't go up as much as I thought it would at low pressures, but ~6% less fuel at 5 psi over stock is very good. Also confirms that pressures over 40 psi don't tend to yield much additional efficiency.

Surprised that no-one has tested this yet on their LEAF should be easy to do using the mi / kWh readout...
 
In my experience - positives / negatives to +5 psi are:

Negatives:
Slightly increased NVH.

Positives:
~5% better fuel economy
Better handling / road feel
More even tire wear (less shoulder wear)

Positives far outweigh the negatives in my experience for a +5 psi inflation. In all my cars I typically run about ~40 psi when the recommended is around 32-35 psi. But never above the max pressure listed on the sidewall - have driven a F150 where the recommended and max pressure was 35 psi so didn't exceed it.
 
I've also found 40 psi to be a good compromise between better mileage and a little stiffer ride. For the minimal increase in range above 40 psi - doesn't seem worth it.


Also - higher PSI is supposed to have a negative impact on braking distance - but I haven't seen any charts which provide the details of how much. If anyone has seen braking distance vs. psi charts for a given car - please post! That would be interesting to see.
 
LTLFTcomposite said:
How much does a set of Leaf tires cost, and how much does overinflating reduce their life?
Click to expand...

Someone said Costco has them for $70 a tire. There's probably a discount if you buy 4. Over inflating can cause the tires to wear in the middle and if you go over +5, then your braking distance increases and your handling isn't as good. Also, you may hydroplane much easier at the higher inflations.
 
LEAFfan said:
Over inflating can cause the tires to wear in the middle and if you go over +5
Click to expand...

Not for modern radials, totally even wear at pressures vastly exceeding the max sidewall pressure printed on the tire.. you will get that wear on old bias-ply tires ... but they are only available for truck applications since they can carry a higher load
 
Herm said:
LEAFfan said:
Over inflating can cause the tires to wear in the middle and if you go over +5
Click to expand...
Not for modern radials, totally even wear at pressures vastly exceeding the max sidewall pressure printed on the tire.. you will get that wear on old bias-ply tires ... but they are only available for truck applications since they can carry a higher load
Click to expand...

I've had 'modern radials' for a long time and when I tried to go 5 pounds higher, they began to wear in the middle, so I had to reduce the pressure. Maybe LLRs won't have this problem since they're made of a harder rubber.
 
Put some air in those tires!

The stock tires have a maximum sidewall rating of 44 PSI, so if you wanted to go from the vehicle recommended pressure of 36 PSI to 41 PSI it would be more than safe to do so.

I've been running at 44 PSI in all four tires since the beginning of April and have noticed that the ride is much "stiffer" now, but I'll have to wait until I can get some good OBD diagnostic gear before I can start doing any definitive M/kWh calculations. :D
 
LakeLeaf said:
Also - higher PSI is supposed to have a negative impact on braking distance - but I haven't seen any charts which provide the details of how much. If anyone has seen braking distance vs. psi charts for a given car - please post! That would be interesting to see.
Click to expand...
Here's what I found on braking distance. The effect appears to be negligible for radial tires from 16 to 48 psi.

http://www.barrystiretech.com/sae800087synopsis.html

Braking Traction: Dry traction is unaffected by inflation pressure, and while wet traction is improved, the effect is small.
Click to expand...
 
I've been running side-wall printed max pressure on my Camry for years, and the Center of the tread is indeed wearing faster than the sides. I dropped it back down to manufacturer (door sticker) pressure to see if it evens out.
 
My rule of thumb has always been to run tires at 10% below the maximum pressure posted on the sidewall, and that usually works out to 40psi. I just brought my Leaf's tires up to that yesterday, and while I didn't do an objective test, I think I saw a modest increase in final estimated range on yesterday's commute. The only real negative to slightly higher pressure (in the 40psi range) is a slightly harsher ride.
 
I run 40 psi in the LEAF, have 20,000 miles on the car, and have some good tread life left.

Just rotated tires again, and the fronts were starting to wear slightly on the outer edge before they went to the rear. I'm thinking that I should be able to get 30K miles or so on the original tires...

One thing I notice about people at work who have a LEAF and run "regular" pressure is that they get severe edge wear, especially as the tire slowly leaks over time and they don't air up...

I keep it at 40 psi...
 
I guess a survey/poll asking what PSI you run your tires at, and how long they lasted would be in order. Might have to use the free version of the Qualtrics survey platform in order to get more flexible polling options. As someone with a new car, I'd love to know what I should be doing.

I usually last at LEAST 55,000 miles on my OEM tires on any car, so hearing 30,000 is somewhat disappointing, but this is my first set of LRRs, so who knows.
 
I run 50 psi in my OEM Ecopias and I'm very happy with the results. No abnormal wear, and the handling is greatly improved. There is a slight increase in NVH, but hardly noticeable and well worth the trade-off.

-Phil
 

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